Cryogenic refrigerator arrangement



Sept. 30, 1969 K. w. COWANS 3,469,409

CRYOGENIC REFRIGERATOR ARRANGEMENT Filed April 5. 1967 4 Sheets-Sheet Kenneth W Cowons,

INVENTOR ORNEY.

P 0, 1969 K. w. COWANS 3,469,409

CRYOGENIC REFRIGERATOR ARRANGEMENT Filed April 5, 1967 4 Sheets-Sheet 1 Fig. 2. 42

Sept. 30, 1969 K. w. COWANS CRYOGENIC' REFRIGERATOR ARRANGEMENT 4 Sheets-Sheet 3 Filed April 5, 1967 Sept, 30, 1969 K. w. cowANs 3, cmrocsmc REFRIGERATOR ARRANGEMENT Filed April 5, 1967 4 Sheets-Sheet 4 L l I l l I /'22 mt v86 l l 84 L I i I I 4o [8 Fig. 5

United States Patent CRYOGENIC REFRIGERATOR ARRANGEMENT Kenneth W. Cowans, Los Angeles, Calif., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed Apr. 3, 1967, Ser. No. 627,985 Int. Cl. FZSb 9/00 US. Cl. 62-6 Claims ABSTRACT OF THE DISCLOSURE A cryogenic refrigerator is provided which uses a sealed housing and closed loop circulation of a cryogenic fluid to produce extremely low temperatures. The refrigerator comprises a cold cylinder and a hot cylinder having outof-phase reciprocating displacers therein. Energy input is provided by a decaying radioactive isotope in a capsule in thermal transfer relation with the hot cylinder. The capsule is provided with .a surrounding envelope of insulation comprising an evacuated vacuum chamber having a plurality of spaced shells of high radiation-reflective material. During refrigerator operation, substantially all of the heat created by the decaying isotope is transferred by conduction, convection, and radiation to the refrigerating fluid in the hot cylinder. Upon refrigerator shutdown, substantially all of the heat energy continually created in the isotope capsule is dissipated to ambient by virtue of radiation from the insulating structure defined.

The invention relates to a refrigerating machine providing refrigerating effect at cryogenic temperatures utilizing a decaying radioisotope as an energy source, the energy released being converted to refrigeration without the production of mechanical Work.

As is well known, many electronic devices require continued maintenance at cryogenic temperature levels to effect proper operation. Some systems employing such devices for reasons of economy or locale of use, require extended operation without service or maintenance attention. An example of such isolated long-term operation is a detecting device in an orbital environment about the earth and used to continuously detect earth source radiation for extended time periods. Other examples may involve systems located in remote geographic areas on earth, such as the arctic. The use of conventional energy sources in such applications has been found prohibitive for many reasons, e.g., Weight, storage metering problems, and the like, many of which are related to the operative environment and expense of launch.

To avoid the necessity of large volume of conventional fuel and yet provide an effective heat source designed for long-term refrigerator operation, the present invention incorporates an appropriate radioactive isotope, the natural decay of which is utilized as a source of energy to provide a heat input to one operating aspect of a cryogenic refrigerator and thus provide the power source to effect cryogenic refrigeration at another operating aspect of the refrigerator.

Persons familiar with the various existing modes of providing cryogenic refrigeration are aware of that type of closed-cycle machine which utilizes a relatively hot cylinder associated with a heat source. Such machines have a cold cylinder and a hot cylinder, the cylinders each containing displacer elements which cycle in the respective cylinders in a determined out-of-phase relationship moving a contained constant volume of refrigerating fluid between the cylinders thereby producing a refrigerating effect at the cold cylinder. Simplified, the energy input at the hot cylinder is used to achieve a refrigerating effect at the cold cylinder.

3,469,409 Patented Sept. 30, 1969 Typically, such a refrigerating machine utilizes, in addition to a heat source, an external power source such as an electric motor to cycle the displacer elements in the respective cylinders to achieve fluid circulation therebetween and, during said cycling, create alternate compression and expansion phases thus providing the desired refrigerating effect. A unique feature of the present invention is that the type of machine here under consideration is modified to utilize a radioisotope as the heat source.

An additional feature of the disclosed invention relates to the fact that appropriate insulation is provided at the heat source so that during conditions of non-refrigerating operation the heat created by the decaying isotope is almost entirely radiated to ambient thereby avoiding excessive temperature levels developing in the operating machine which could cause machine failure or failure of the capsule containing the isotope. Because of the presence of radiation a high safety factor is desirable and necessary. During operation as a refrigerator virtually all of the heat generated is utilized in the refrigerating cycle with a minimum being radiated to ambient.

These and other advantages and features of the invention will become apparent in the course of the following description and from an examination of the related drawing wherein:

FIGURE 1 is an isometric view of a structure embodying the invention;

FIG. 2 is a view of the structure of FIG. 1 taken along line 2-2 and partially in elevation partially fragmented to illustrate the internal construction of the arrangement;

FIG. 3 is a view taken along line 33 of FIG. 2 again partially fragmented to show internal construction details;

FIG. 4 is a detailed end view of a heat source capsule employed in the invention; and

FIG. 5 is a fragmentary view taken along line 55 of FIG. 4.

Describing the invention in detail and directing attention to FIGS. 1 and 2, a mounting housing is indicated generally at 10 and is used to support the entire arrangement. The numeral 12 generally indicates a refrigerating machine of the type here under consideration which comprises a sealed housing 14 having an electric motor or main drive source 16 conventionally secured to the housing 14. A hot cylinder is indicated at 18 and a refrigerating or cold cylinder at 20, the details of which will be subsequently described. A heat source capsule or fuel cylinder is shown at 22 and may be integrally formed with the cylinder 18.

Referring to FIGS. 2 and 3, the conventional power source or electric motor is shown at 16 and is provided with an output shaft 24, the latter having an eccentric crank at 26 is journalled as at 28 to a first connecting rod 30, the later being journal pin connection, as at 32, with a hot cylinder displacer 34. Again, it is noted the numeral 18 indicates the hot cylinder.

The crank 26 is also journally connected as at 32 to a second connecting rod 35, the later being conventionally connected to a displacer element 36 located in the cold cylinder 20. It will be understood, of course, that the displacer elements 34 and 36 reciprocate within the respective cylinders 18 and 20 upon rotation of the eccentric crank 26 in response to power received from motor 16.

The hot cylinder 18 defines a hot chamber 40 therein. Physically joined to or integrally formed with the hot cylinder 18 is the fuel cylinder 22, the latter defining a plurality of cavities 42, 42, as hereinafter will be described. The fuel cylinder 22 is preferably formed of a high thermal transfer material such as copper, or the like, whereby heat generated will be readily transferred to the chamber 40.

As noted, the cylinder 18, with the chamber 40 disposed therein, accommodates the reciprocating motion of a hot displacer element 34. A communicating path is provided from chamber 40 along a channel 50 formed in the wall of cylinder 18 to an annular channel 52, the latter formed in main housing 14. Channel 52 is in communication with the working volume 54 defined by housing 14 and containing the eccentric crank 26 and related connecting rods. This communication is established by passage 56. As Will be seen in FIG. 3, passage 52 communicates with a necked-down segment 58 of cold displacer 36. The necked-down segment 58 is provided with openings 60, the latter establishing communication with a first regenerator passage 62 formed internally of the cold displacer 36. Communcation is established between the first regenerator 62 and a first stage expansion chamber 64 via opening 66 defined in displacer 36. The displacer 36 is provided with an extended reduced diameter cylindrical segment 68, the latter reciprocating within a second stage expansion chamber 70 formed in cylinder 20. Communication is established between expansion chamber 64 and expansion chamber 76 via a second stage regenerator 72 contained by cylinder and communicating with chamber 64 via opening 74. Passage 50 may have regenerator material (not shown) disposed therein to achieve the functional effect hereinafter described.

Briefly describing the operation of the refrigerating machine here under consideration, it will be understood that the chamber will be termed a hot chamber while the expansion chambers 64 and 70 will collectively be termed cold chamber. In view of the fact that the passage 52 communicates with the chamber 54, that is, the working volume defined by housing 14, and that refrigerating fluid is free to circulate therein, the chamber 54 will be termed cool chamber. The hot chamber, the cool chamber, and the cold chamber are, of course, filled with a refrigerating fluid so that the entire system is completely closed.

In normal operation, heat is supplied to the hot chamber 40 and as a result the pressure and the temperature of the refrigerating fluid therein is raised. Assuming that the expansion displacer element 36 is at bottom-deadcenter and that the hot displacer element 34 is at intermediate stroke, continued rotation of the crank 26 in response to rotary action of the motor 16 will move the cold displacer 36 to an intermediate position within cylinder 20 and bring the hot displacer 34 to a top-deadcenter position in chamber 40. Movement of the displacer element 34 forces the gas in chamber 40 through passage 50 and the regenerating material disposed therein to the working volume or cool chamber 54. In passing through the passage 50, the relatively hot fluid is cooled by dissipating a major segment of its heat to the regenerating material in passage 50. Thus, movement of the fluid from chambers 40, 64, and 70 to cool chamber 54 is achieved at relatively constant pressure. This is the result of the cooling effect of gas passage through the regenerator material.

Continued motion of crank 26 moves the cold displacer 36 to top-dead-center position while hot displacer 34 is returned to a central position in cylinder 18. This movement of the displacers forces the gas in the system from chambers 64 and 70 through the regenerators 72 and 62 and from the cool chamber 54 through the passage 50 and regenerating material contained therein to the chamber 40. Movement of the fluid through the regenerators 72 and 62 increases the temperature thereof as the fluid absorbs heat from the regenerator and movement of the fluid through passage 50 increases its temperature again as a result of heat absorption from the regenerator material located herein. This brings the fluid in the system to a maximum working pressure. Continued rotation of the crank 26 moves the cold displacer 36 to an intermediate position and the hot displacer 34 to a bottom-dead-center position in their respective cylinders. As a result of this motion, the fiuid within chambr 54 is moved therefrom and passes through passage 50 and the regenerator material contained therein to the chamber 46'. Concurrently, a smaller portion of the fluid within chamber 54 may pass through passage 52, regenerator 62, and regenerator 72 and into expansion chambers 64 and 70. Fluid passing into chambers 64 and 70 is cooled as a result of passage through the regenerators and the cooling existing concurrently with the maximum volume in chamber 40 reduces the fluid pressure in the entire system.

Continued rotation of the crankshaft 26 brings the cold displacer 36 to bottom-dead-center position and moves hot displacer 34 to an intermediate position on its compression stroke. Movement of the displacer element 34 induces some fluid to move from chamber 40 through passage 50 and through the cooling regenerator material therein to chamber 54. Continued expansion of the fluid in chambers 64 and 70 results in further cooling thereof and achieves the ultimate refrigerating effect at cylinder 20.

As described, the refrigerating effect is achieved by virtue of the energy resulting from heat input to chamber 40 from an adjacent source. The power from the electric motor 16 is merely used to cycle the displacer elements 34 and 36 and achieve refrigerant flow as above described.

Considering FIG. 2 and FIGS. 4 and 5, the fuel cylinder 22 is there shown in detail. The present invention provides as a heat source a radioactive isotype that releases energy either as a result of the continuous transition of nuclei, either to another nuclei or to a lower energy state in the original nucleus. There are several isotopes currently available which meet the appropriate fuel parameters for this application. Plutonium or plutonium oxide are examples though others may be effectively used.

In the radioactive transition described above, the accompanying radiation carries energy away from the transforming nucleus. This energy will exist in the form of alpha particles, beta particles, and gamma rays, the last being electromagnetic radiation, The present invention suggests the formation of isotope fuel cylinder 22 as an integral extension of hot cylinder 18, the cylinder 22 having a plurality of cavities formed therein. Each cavity 80 contains an appropriate quantity of the selected radioactive material. Again, it is noted that the material forming cylinder 18 and housing 22 be highly thermally conductive, for example, copper or iron. The energy released by the isotopic material in chambers 80 is absorbed by wall segments 82, 84, and 86. As a result of such absorption, the energy in transition is transformed into heat, that is, the respective Wall segments 82, 84, and 86 are heated. The heat is transferred by thermal conduction through the walls to the hot chamber 40 where, by virtue of radiation, convection, and conduction, the refrigerating fluid within chamber 40 is heated. Thus, the necessary energy input is provided to achieve the refrigerating effects desired. Depending upon the level of refrigeration desired, the amount of radioactive fuel disposed in the cavities 80 may be carefully regulated.

Returning to FIG. 2, it will be recalled that a feature of the invention involved a mode of dissipating the heat generated by the decaying radioisotope in cylinder 22 during those time periods when the refrigerator is not operating. In view of the high thermal conductivity of the wall of cylinder 22 and hot cylinder 18, virtually all of the heat created as a result of radioactive transition will be absorbed by the gas in chamber 40 during refrigerator operation.

An insulation barrier is provided at 90 surrounding cylinder 22. The insulation 90 should have such an energy transfer quality that it will provide a heat transfer path more difiicult to traverse than the thermal transfer path through the segments 82, 84, and 8-6 to the chamber 40 during refrigerator operation, When the refrigerator is not operating, the temperature in the housing 22 will rise to a determined level whereat the heat will conductively transfer through the insulation 90 and be radiated to ambient preventing a rise in machine temperature beyond a certain maximum. Thus, in the non-refrigerating operating mode, the created heat, which is continuous as a result of the continuous transition of the radioactive isotope, will be radiated to ambient and deleterious effect on the structure avoided.

One mode, a preferred one, of effecting proper insluation of the capsule 22 is by the incorporation of multilayer radiation shields. For example, the outer cylinder 93 may be spaced from the capsule 22 and the atmosphere therebetween evacuated to provide a vacuum condition. Numeral 89 indicates the evacuated space. Within the space 89 a plurality of radiation shields 91, 91, are concentrically provided. The shields 91 and 93 are preferably highly reflective. It is desirable that the material used to fabricate shields 91 and 93 have a quality whereby surface thermal radiation emissivity increases markedly with temperature increase. Nickel is an appropriate material though others would occur to persons familiar with this art. In the structure described, heat energy passing from the capsule 22 to ambient through the shields 91 and 93, and under refrigeration non-operating conditions, would be approximately proportional to the fourth power of the absolute temperature of the radioisotopecontaining capsule 22. This, of course, assumes an ambient temperature condition less than capsule temperature condition.

In normal operation, therefore, the heat generated in the walls 82 and 86 as a result of isotope decay, as above described, would be conductively transferred through said walls to the chamber 40 to there heat the cryogenic fluid by conduction, convection, and radiation, In this circumstance, virtually none of the created heat would pass to ambient through the shields 91 and 93 as the path of least thermal resistance is directly to the chamber 40. As an example, and with a typical refrigerator in normal operation, the capsule 22 would be at a temperature level of approximately 1000 F. and maintain that approximate level as a result of heat transfer to the refrigerating fluid. Upon refrigerator shutdown, the radioisotope would continue to decay, generating heat in the walls 82, 84, and 86 of the capsule 22. The temperature of the capsule, therefore, would rise appreciably, for instance, as in the example above, to a level of about 2000 F. Under these circumstances, radiation would be emitted from the capsule 22 through adjacent evacuated space to the inner cylinder 91, and from the inner cylinder 91 through evacuated space to the outer cylinder 91 and again from the outer cylinder 91 through the evacuated space to the enclosing cylinder 93 from whence it would be radiated to ambient. Using this mode of heat transfer and in view of the fact that heat dissipation is proportional to approximately the fourth power of absolute temperature of the capsule 22, virtually all of the heat energy created would be dissipated to ambient by the radiation sequence described. With this arrangement, the progressively increasing capacity to dissipate generated heat to ambient in response to minimal temperature rise assures that the heat gene-rated during non-refrigerating periods will be effectively dissipated without important temperature change avoiding capsule damage or failure or injury to the operating parts of the refrigerator The invention as shown and described is by way of illustration and not limitation and may be modified in many particulars all within the spirit and scope thereof.

What is claimed is:

1. In a cryogenic refrigerating device to provide refrigerating effect at cryogenic temperatures by utilizing heat energy input source,

the combination of a sealed housing,

said housing defining a hot cylinder at one aspect thereof and a cold cylinder at another aspect thereof,

a working chamber defined by the housing intermediate the hot and cold cylinders and having crankshaft means journaled for rotation therein,

a first displacer in the hot cylinder defining with the cylinder a hot chamber and a second displacer in the cold cylinder defining therewith a cold chamber,

passage means establishing communication between the hot chamber and the working chamber, and

other passage means establishing communication between the cold chamber and the working chamber,

regenerator means in the respective passage means,

juncture means establishing communication between the respective regenerator means at point of entrance of the passage means to the Working chamber,

a heat load associated with the cold cylinder,

and heat input means associated with the hot cylinder,

said heat input means comprising a container having a radioactive isotope disposed therein,

said isotope being operative to decay and continuously release energy, and

means to capture the released energy and thermally transfer the heat created thereby to the hot chamber of the hot cylinder.

2. A cryogenic refrigerating device according to claim 1,

wherein said heat input means container includes metallic walls surrounding the decaying radioisotope to receive emitted radiation therefrom and be heated as a result of the impingement of said radiation,

said walls providing a thermally conductive heat path to the hot cylinder.

3. A cryogenic refrigerating device according to claim 2,

wherein said heat input means container is integrally formed with said hot cylinder and in immediate juxtaposition therewith.

4. A cryogenic refrigerating device according to claim 3, and

including insulation means surrounding said heat input means container,

said insulation means providing a heat dissipation path to ambient of a higher thermal resistance than the thermal heat transfer path between the container and the hot cylinder,

whereby, upon operation of the refrigerating device, substantially all of the heat energy created as a result of the decaying radioisotope is transferred to the hot cylinder.

'5. A cryogenic refrigerating device according to claim 4,

wherein the insulation is operative to transfer to ambient heat energy created as a result of the decaying radioisotope in the heat source during periods of refrigerator non-operation to maintain the temperature rise of the refrigerating device within predetermined limits.

6. A cryogenic refrigerating device according to claim 5,

wherein said insulation comprises a vacuum space surrounding said heat input means container,

said vacuum space containing energy radiating shield means disposed therein and normally spaced from said container.

7. A cryogenic refrigerating device according to claim 6,

wherein said radiating shield means comprises a plurality of annular radiating plates surrounding said heat input means container.

8. In a refrigerating device to provide refrigerating efiect by utilizing a heat energy input source,

a combination of a housing defining a hot cylinder at one aspect and a cold cylinder at another aspect thereof,

said cylinders having reciprocating displacers disposed therein,

a cool chamber defined by said housing,

means establishing communication between the cool chamber and the hot and cold cylinders, respectively,

means connected to the respective displacers to induce reciprocation thereof in out-of-phase relationship,

heat input means thermally associated with the hot cylinder and comprising a container having a decaying radioactive isotope therein,

said isotope being operative to release energy as a result of said decaying action,

means to capture said released energy and thermally transfer same to the hot cylinder durin refrigerating device operation, and

insulation means shielding said container from ambient to inhibit the transfer of said released energy to ambient during refrigerator device operation.

9. A refrigerating device to provide refrigerating effect by utilizing a heat energy input source according to claim 8,

wherein said insulation means comprises a vacuum surrounding said container, and

radiation shield means disposed in the vacuum and normally spaced from the container.

10. A device to provide refrigerating effect by utilizing heat energy input source according to claim 9,

References Cited UNITED STATES PATENTS 2,484,392 10/1949 Van Heeckeren 626 2,803,951 8/1957 Newton 626 2,993,341 7/1961 Newton 626 3,029,596 4/1962 Hanold 626 WILLIAM J. WYE, Primary Examiner US. Cl. X.R. 

